U.S. patent number 6,796,179 [Application Number 10/441,892] was granted by the patent office on 2004-09-28 for split-resonator integrated-post mems gyroscope.
This patent grant is currently assigned to California Institute of Technology. Invention is credited to Youngsam Bae, Ken J. Hayworth, Kirill V. Shcheglov.
United States Patent |
6,796,179 |
Bae , et al. |
September 28, 2004 |
Split-resonator integrated-post MEMS gyroscope
Abstract
A split-resonator integrated-post vibratory microgyroscope may
be fabricated using micro electrical mechanical systems (MEMS)
fabrication techniques. The microgyroscope may include two
gyroscope sections bonded together, each gyroscope section
including resonator petals, electrodes, and an integrated half
post. The half posts are aligned and bonded to act as a single
post.
Inventors: |
Bae; Youngsam (Gardena, CA),
Hayworth; Ken J. (Northridge, CA), Shcheglov; Kirill V.
(Los Angeles, CA) |
Assignee: |
California Institute of
Technology (Pasadena, CA)
|
Family
ID: |
31997191 |
Appl.
No.: |
10/441,892 |
Filed: |
May 16, 2003 |
Current U.S.
Class: |
73/504.12;
438/50 |
Current CPC
Class: |
G01C
19/5719 (20130101) |
Current International
Class: |
B81C
3/00 (20060101); G01C 19/56 (20060101); G01P
009/04 () |
Field of
Search: |
;73/504.12,504.02,504.04
;438/50 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chapman; John E.
Attorney, Agent or Firm: Fish & Richardson P.C.
Government Interests
ORIGIN OF INVENTION
The U.S. Government has certain rights to this invention pursuant
to Grant No. NAS7-1407 awarded by the National Aeronautics &
Space Administration (NASA).
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to U.S. Provisional Application
Ser. No. 60/381,630, filed on May 17, 2002 and entitled Split
Resonator Integrated Post MEMS Gyroscope.
Claims
What is claimed is:
1. An apparatus comprising: an upper gyroscope section including a
resonator section including a plurality of resonator petals and an
integrated half post section, and a base section including a
plurality of electrode sections, each electrode section including
one or more electrodes; and a lower gyroscope section, the lower
gyroscope section including a resonator section including a
plurality of resonator petals and an integrated half post section,
the half post section being aligned with the half post section in
the upper gyroscope section, and a base section including a
plurality of electrode sections, each electrode section including
one or more electrodes.
2. The apparatus of claim 1, wherein each resonator petal in the
upper gyroscope section is aligned with an electrode section in the
lower gyroscope section, and wherein each resonator petal in the
lower gyroscope section is aligned with an electrode section in the
upper gyroscope section.
3. The apparatus of claim 2, wherein the aligned resonator petals
and electrode sections are separated by a distance approximately
equal to a thickness of a resonator section.
4. The apparatus of claim 1, wherein the upper gyroscope section is
bonded to the lower gyroscope section.
5. The apparatus of claim 1, wherein the apparatus comprises a
micro electrical mechanical systems (MEMS) device.
6. The apparatus of claim 1, wherein each of the upper and lower
gyroscope sections include three resonator petals and three
electrode sections.
7. The apparatus of claim 1, wherein the upper and lower gyroscope
sections include drive electrodes and sense electrodes.
8. The apparatus of claim 1, wherein each resonator section
includes: an outer ring; a hub supporting the integrated half post
and the resonator petals; and a plurality of spring members
connecting the hub to the outer ring.
9. A method comprising: etching a pattern defining alternating
resonator petals and electrode sections into a top silicon layer of
a first silicon-on-insulator wafer section; etching a pattern
defining alternating resonator petals and electrode sections into a
top silicon layer of a second silicon-on-insulator wafer section;
forming electrodes on the electrode sections of the first and
second wafer sections; etching a bulk silicon section of the first
wafer section to form a frame and an integrated half post; etching
a bulk silicon section of the second wafer section to form a frame
and an integrated half post; bonding the first and second wafer
sections such that the half posts are aligned and bonded to form a
split-post microgyroscope.
10. The method of claim 9, further comprising: etching the
insulator in the first wafer section to release the resonator
petals; and etching the insulator in the second wafer section to
release the resonator petals.
11. A vibratory microgyroscope comprising: an upper gyroscope
section including a resonator section including an outer ring, a
hub connected to the outer ring by spring members, a plurality of
resonator petals connected to the hub, and an integrated half post
connected to the hub, a base section including a plurality of
electrode sections, each electrode section including at least one
of a drive electrode and a sense electrode; and a lower gyroscope
section including a resonator section including an outer ring, a
hub connected to the outer ring by spring members, a plurality of
resonator petals connected to the hub, and an integrated half post
connected to the hub, a base section including a plurality of
electrode sections, each electrode section including at least one
of a drive electrode and a sense electrode, wherein the lower
gyroscope section is bonded to the upper gyroscope section such
that the integrated half posts are aligned.
12. The microgyroscope of claim 11, wherein each resonator petal in
the upper gyroscope section is aligned with an electrode section in
the lower gyroscope section, and wherein each resonator petal in
the lower gyroscope section is aligned with an electrode section in
the upper gyroscope section.
13. The microgyroscope of claim 12, wherein the aligned resonator
petals and electrode sections are separated by a distance
approximately equal to a thickness of a resonator section.
14. The microgyroscope of claim 11, wherein the microgyroscope
comprises a micro electrical mechanical systems (MEMS) device.
15. The microgyroscope of claim 11, wherein each of the upper and
lower gyroscope sections include three resonator petals and three
electrode sections.
Description
BACKGROUND
Multi-axis sensors may be used for inertial sensing of motion in
three dimensions. Such sensors may be constructed of relatively
large and expensive electromagnetic and optical devices. More
recently, micromechanical sensors have been fabricated using
semiconductor processing techniques. Micro electrical mechanical
systems (MEMS) allow formation of physical features using
established semiconductor materials and processing techniques.
These techniques enable the physical features to have relatively
small sizes and be precise. Specifically, micromechanical
accelerometers and gyroscopes have been formed from silicon wafers
using photolithographic and etching techniques. Such
microfabricated sensors hold the promise of large scale production
and lower cost.
Vibratory microgyroscopes ("microgyros") have been produced using
MEMS processing techniques. In a vibratory gyroscope, the Coriolis
effect induces energy transfer from a driver input vibratory mode
to another mode which is sensed or output during rotation of the
gyroscope. Silicon micromachined vibratory microgyros may be
integrated with silicon electronics. These devices are capable of
achieving high quality (Q) factors, can withstand high "g" shocks
due to their small masses, are relatively insensitive to linear
vibration, and consume little power. However there are several
limitations to the current construction method that hinders its
mass producability, specifically each microgyro must have a post
inserted and bonded individually to function.
SUMMARY
A vibratory microgyroscope may include an upper gyroscope section
bonded to a lower gyroscope section. Each gyroscope section may
include resonator petals, electrodes, and an integrated half post.
The half posts are aligned and bonded to act as a single post.
The gyroscope sections may have a symmetrical design, each include
three resonator petals alternating with three electrode sections.
The electrodes sections may include drive and sense electrodes for
driving and sensing rocking modes, respectively. Each gyroscope
section may include a hub connected to an outer ring by spring
members. The hub may support the resonator petals and the
integrated half post.
The vibratory microgyroscope may be a micro electrical mechanical
system (MEMS) device fabricated from silicon-on-insulator (SOI)
wafer(s) using semiconductor processing techniques.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective sectional view of a vibratory
microgyroscope.
FIGS. 2A-2D show side, bottom, top, and perspective views,
respectively, of an upper gyroscope section.
FIGS. 3A-3D show side, bottom, top, and perspective views,
respectively, of a lower gyroscope.
FIGS. 4A and 4B show sectional views of silicon-on-insulator (SOI)
wafer sections used to form upper and lower gyroscope sections.
FIGS. 5A and 5B show sectional views of the SOI wafer sections
after an etching process to form a clover-leaf resonator petal
pattern in a silicon layer.
FIGS. 6A and 6B show sectional views of the SOI wafer sections
after an electrode deposition process.
FIGS. 7A and 7B show sectional views of the SOI wafer sections
after an etching process to form a frame and integrated half post
in the bulk silicon section of the SOI wafer sections.
FIGS. 8A and 8B show sectional views of the upper and lower
gyroscope sections after an etching process to separate the
resonator petals.
FIG. 9 shows a sectional view of the vibratory microgyroscope.
DETAILED DESCRIPTION
FIG. 1 is a perspective sectional view of a vibratory
microgyroscope 100 according to an embodiment. The microgyroscope
may have a split design including an upper gyroscope section 105
and a lower gyroscope section 110. Each of the sections may be
fabricated from a silicon-on-insulator (SOI) wafer, as will be
described below. FIGS. 2A-2D show side, bottom, top, and
perspective views, respectively, of the upper gyroscope section
105, and FIGS. 3A-3D show side, bottom, top, and perspective views,
respectively, of the lower gyroscope section 110.
Each gyroscope section includes a resonator section 205 including
three resonator "petals" 210 offset by 60 degrees, and a base
section 215 including three electrode sections 220. Each gyroscope
section may also include an integrated half post 225. The resonator
petals and half post may be supported by thin resonator springs 230
connecting a hub 235 and the half post 225 to an outer ring 240 in
the resonator section. The electrode sections include electrodes
245 used for driving and sensing rocking modes.
The upper and lower gyroscope sections may be bonded together such
that the resonator petals 210 of each gyroscope section overlap the
electrode sections 220 of the other gyroscope section and the half
posts 225 are aligned to form a split post. A capacitive gap
between the petals and electrodes may be formed by the opposing
resonator section's thickness.
In operation, a potential between the electrodes 245 and the petals
210 pulls the petals closer to the electrodes due to electrostatic
forces. This rocks the assembly about a drive axis. Since the
resonator is symmetrical, the axis may be the y-axis, x-axis, or a
combination of the two. The large post adds inertia to the rocking
modes, which aids in coupling the degrees of freedom. Excitation at
the drive axis natural frequency may be desirable, since a large
response is obtained which boosts the sensitivity of the device.
Angular rotation of the frame about the z-axis induces post rocking
(via Coriolis acceleration) about a sensing axis orthogonal to the
z-axis and the drive axis (e.g., the x-axis if the y-axis is the
drive axis). The rocking about the sense axis may be measured
capacitively by electrodes 245 on the electrode sections 220. These
measurements are related to the angular rate of rotation of the
frame.
Typical microgyroscopes require a post (metal or silicon) to be
inserted and bonded individually. With the split resonator design,
an individual post insertion step is not required, which may
facilitate mass-production of the microgyroscopes. The two
integrated half posts align to serve as a single post. Both halves
of the post are supported by the resonator springs 230 along the
midline of the respective gyroscope section, and thus no separate
supports are necessary.
The upper and lower gyroscope sections may be fabricated from
silicon-on-insulator (SOI) wafers 400, e.g., with a 500 micron bulk
silicon substrate 405 and a 10 micron silicon oxide membrane 410,
as shown in FIGS. 4A and 4B. The cloverleaf design of the petals
may be etched into the top silicon layer 415 of the SOI wafer using
precision etching techniques, as shown in FIGS. 5A and 5B. In
similar SOI cloverleaf microgyro designs, etching equipment from
Surface Technology Systems plc (STS) of Newport, UK has been used
for the precision etching.
Electrodes 420 may then be deposited and patterned on the insulator
membrane in the electrode sections, as shown in FIGS. 6A and 6B.
The electrodes may be, e.g., thin film Cr/Au electrodes deposited
by thermal evaporation of chromium and gold. Thin film metal layers
may also be deposited at feed-through sites 425 and eutectic
bonding sites 430 during the thermal evaporation process. The bulk
silicon substrate may then be etched to form a frame including the
electrode sections 440 and the half post 450 for that section, as
shown in FIGS. 7A and 7B. Portions of the oxide membrane 410 may
then be etched to free the resonator petals 455, as shown in FIGS.
8A and 8B.
The gyroscope may be assembled by eutectic-bonding the upper and
lower gyroscope sections at the eutectic bonding sites 430 and
wire-bonding the feed-throughs 425 to the electrodes 420, as shown
in FIG. 9.
As described above, the split design of the split-resonator
integrated-post MEMS gyroscope may facilitate mass-production of
the microgyros. Since an individual post insertion step is
unnecessary, the processing steps and time may be independent of
the number of devices being produced. Consequently, an entire wafer
full of devices may be processed simultaneously.
In alternative embodiments, the resonator section may include
different numbers and arrangements of petals and electrodes. The
electrode sections may include more than one electrode. Different
electrodes on each or different electrode sections may be used for
driving and sensing rocking modes.
A number of embodiments have been described. Nevertheless, it will
be understood that various modifications may be made without
departing from the spirit and scope of the invention. Accordingly,
other embodiments are within the scope of the following claims.
* * * * *